Preparation:
Quarter the apples, remove the cores, and slice them very thinly using a sharp knife or a mandoline. Place the apple slices in a saucepan, cover with water, add the lemon juice and sugar, and simmer for about 2 minutes. Drain and let them dry well.
Preheat the oven to 160 °C (320 °F) convection / fan-assisted.
Cut each sheet of puff pastry lengthwise into 6 strips and spread with jam. Arrange the apple slices along the top edge of each strip so that they overlap and protrude by about half. Fold the lower half of the pastry strip up over the apples and carefully roll up.
Grease a muffin tin with a little butter or oil. Place the apple roses into the wells and bake on the lowest rack for 30 minutes.
Dust with decorating sugar before serving.